Generally, in a dry process electrophotographic copying machine of the Xerographic or similar type, subsequent to projection of light images of an original to be copied onto a preliminarily charged photoreceptor surface for the formation of an electrophotographic latent image of the original thereon, the latent image is developed into a visible toner powder image by a developing apparatus disposed along the path of the photoreceptor. Accommodated in a housing of such a known developing apparatus are developing material composed of magnetizable carrier material and electroscopic toner powder, and a developing roller rotatably disposed adjacent to and in spaced relation to the photoreceptor and having a rotatable outer cylinder and a plurality of stationary magnets fixedly disposed in the outer cylinder for the formation of magnetic brush bristles of the developing material on the outer cylinder, which brush bristles rub against the latent image on the photoreceptor to develop the same into the visible toner powder image for subsequent transfer thereof onto transfer material such as copy paper. The toner dispensing device includes a toner tank filled with toner powder or toner particles which are supplied at predetermined rates into the housing of the developing apparatus for being mixed with the developing material housed in said housing and supplied onto the developing roller through developing material stirring and supplying means disposed adjacent to said developing roller. In the arrangement as described above, it is commonly required that the toner dispensing device be capable of supplying the toner particles at constantly uniform rates, with the toner particles being simultaneously prevented from undergoing the undesirable bridging phenomenon in the toner tank. On the other hand, following the general trend to increasing copying speeds in electrophotographic copying apparatuses, troublesome procedures for frequently replenishing the toner tank with toner powder are inevitably involved. In order to eliminate such inconveniences, large toner tanks tend to be employed, in which case, however, if a large amount of toner powder is housed in a toner tank, the density of toner powder at the lower portion of the toner tank increases due to the weight of the toner powder itself, and thus the amount of toner powser supplied through the lower portion of the toner powder supplied through the lower portion of the toner tank consequently increases due to its high density. However, when the amount of the toner powder in the toner tank is reduced through consumption, the toner powder around the lower portion of the toner tank is less affected by its weight, with consequent low density of the toner powder thereat and reduction in the amount supplied to the developing apparatus. In other words, due to the increase of toner tank size, the amount of toner powder to be supplied to the developing device varies depending on the amount of the toner housed in the toner tank, with consequent variations of toner concentration in the developing material housed in the developing apparatus housing. Such inconveniences not only result in unfavorable development, but also in hardening of the toner powder due to the high density thereof when a large amount of toner is housed in the toner tank.
In order to supply toner powder at predetermined constant rates, there has conventionally been proposed, for example, by IBM Technical Disclosure Bulletin (Vol. II No. 5 October 1968), a toner dispensing device as shown in FIGS. 1A to 1C. The prior art toner dispensing device includes a hopper or toner tank H filled with toner powder t for dispensing the toner at a predetermined rate into a developing chamber (not shown) of a copying machine. The hopper H further includes a pair of downwardly converging side walls Ha and Hb and a bottom wall formed by a resilient flap Hf and a spring member Hs which engages the flap Hf adjacent to its point of contact with the wall Ha of the hopper H, while a vertically movable dispensing member D is disposed within the hopper H and adjacent to the wall Ha. The dispensing member D urged by a spring Ds upwardly against a stationary stop Hp has a dispensing blade portion Db which rides against the wall Ha of the hopper H, with a cam follower portion Dc which extends from the dispensing member D and which is engaged by a rotatable cam C. For dispensing the toner t, the cam C is rotated and as shown in FIG. 1B, a measured amount of toner t is trapped between the end of the blade Db, the wall Ha of the hopper H, and the flap Hf. The toner t thus trapped is dispensed as the flap Hf is deflected upon continued downward movement of the blade Db as shown in FIG. 1C. The cam C is formed with a notch Cb which causes an abrupt jump in the blade Db while it is below the flap Hf to ensure that the toner t is removed from the end of said blade Db, and the feed rate is varied by adjusting the angular position of the flap Hf to change the volume of the enclosure formed by the wall Ha of the hopper H, flap Hf and the lower end of the blade Db. The known toner dipensing device as described above, however, still has a disadvantage in that it is rather difficult to supply a constantly uniform amount of toner at all times due to its construction and supplying method based on the jumping action of the blade Db, and in that the undesirable bridging phenomenon of the toner within the toner tank H is not sufficiently prevented.
Furthermore, in conjunction with the foregoing arrangements of the conventional toner dispensing devices, the prior art developing meterial stirring and supplying means employed in the known developing apparatus is imperfect in its performance for stirring and supplying the developing material, with the toner particles not being uniformly and sufficiently charged tribo-electrically by the carrier material, thus resulting in various inconveniences in achieving optimum development.